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58 lines
2.0 KiB
58 lines
2.0 KiB
2 years ago
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C Copyright(C) 1999-2020 National Technology & Engineering Solutions
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C of Sandia, LLC (NTESS). Under the terms of Contract DE-NA0003525 with
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C NTESS, the U.S. Government retains certain rights in this software.
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C
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C See packages/seacas/LICENSE for details
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C=======================================================================
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LOGICAL FUNCTION ZAWAY (NLNKF, LINKF1, XN, YN, ZN, HIDENP)
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C=======================================================================
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C --*** ZAWAY *** (MESH) Determine if face is hidden
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C -- Written by Amy Gilkey - revised 10/22/87
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C -- Sam Key, 03/01/85
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C --
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C --ZAWAY determines if a face on a 3D surface is hidden.
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C --It is hidden if and only if its outward normal points "into" the
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C --plotting surface. Nodes within the face are marked as
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C --visible if the face is visible.
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C --
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C --Parameters:
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C -- NLNKF - IN - the number of nodes per face
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C -- LINKF1 - IN - the connectivity for the face
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C -- XN, YN, ZN - IN - the nodal coordinates; the Z-coordinate is
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C -- pointing towards the viewer (out of the plotting plane)
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C -- HIDENP - IN/OUT - node status (as in HIDDEN)
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PARAMETER (KNVIS=0, KNFOVR=10, KNHID=100)
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INTEGER LINKF1(NLNKF)
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REAL XN(*), YN(*), ZN(*)
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INTEGER HIDENP(*)
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C --Form X and Y components of diagonal vectors of face
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C --(calculate from midpoint of each side)
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AX = (XN(LINKF1(3)) + XN(LINKF1(4)))
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& - (XN(LINKF1(1)) + XN(LINKF1(2)))
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BX = (XN(LINKF1(4)) + XN(LINKF1(1)))
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& - (XN(LINKF1(2)) + XN(LINKF1(3)))
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AY = (YN(LINKF1(3)) + YN(LINKF1(4)))
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& - (YN(LINKF1(1)) + YN(LINKF1(2)))
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BY = (YN(LINKF1(4)) + YN(LINKF1(1)))
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& - (YN(LINKF1(2)) + YN(LINKF1(3)))
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C --Form Z component of normal vector to corner, and make node
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C --visible if normal points forward
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ZAWAY = (AX*BY .LE. BX*AY)
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IF (.NOT. ZAWAY) THEN
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DO 100 ILINK = 1, 4
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HIDENP(LINKF1(ILINK)) = KNVIS
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100 CONTINUE
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END IF
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RETURN
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END
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